The Trezevant High School principal who uncovered a grading scandal at the school last year is resigning from Shelby County Schools over the way he says the district handled the investigation.

Ronnie Mackin sent a letter to board members and Superintendent Dorsey Hopson alleging he was brought in to the school to be a "scapegoat" for "corrupt, illegal, and unethical activities" by district staff.

He also alleges the district was removing him from his position as principal due to "safety concerns" after his car was vandalized, and that he received threats to himself and his assistant principals. But Mackin said he expected to accept another job in the district. His resignation is effective July 1.

Mackin, who is also a Millington Municipal Schools board member, called the situation at Trezevant "dire" and said problems are not limited to his school, which is part of the district's Innovation Zone turnaround program.

"There have been multiple incidents where I have uncovered illegal and unethical wrongdoings and was basically told to not comment on it," Mackin said in his six-page resignation letter.

In August, Mackin notified the district he'd found discrepancies in students' transcripts that didn't match the grades students had earned. The district launched an investigation.

"Parents immediately started asking questions, demanded answers, and expressed their frustrations toward me and my administrative team," Mackin said. "Parents demanded that I be fired and removed from the school."

The investigation resulted in the termination of Shirley Quinn, who was accused of "falsifying student records by making unauthorized changes to student transcripts," according to the district's investigation report released in November, and making "inappropriate transcript edits to approximately 33 current" student transcripts.

It also states transcript changes made under Quinn's login in the district's software system began in 2012.

Mackin started at the school in August. He was previously principal of Raleigh-Egypt Middle School.

Mackin alleged there are "multiple student-athletes now enrolled in colleges and universities who did not have appropriate credits to graduate or attend college."

"Their GPA’s were inflated along with being provided credits for classes they did not pass," Mackin wrote.

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White announced in March he was moving to Melrose High to coach football, but Mackin alleges in his letter he fired White after White allegedly "embarrassed" the school in front of a crowd of people on National Signing Day.

It was during the ceremony, White said that his vehicle was vandalized with racial slurs. Mackin is white, and the majority of the student body at the school is black.

White did not immediately return a phone call seeking comment. Mackin said he could not comment beyond what was in his letter.

In the letter, Mackin also said a district official questioned him regarding missing money from the school, but Mackin told the official he wasn't in the building because he was taking a leave of absence following the sudden death of his daughter in February.

In response to Mackin's resignation letter, SCS released the following statement Thursday afternoon:

"SCS received Ronnie Mackin’s letter concurrent with the letter being provided to the media. The letter’s import is clouded by Mackin’s prior demand that SCS pay him 2 years of severance pay, and his inability to provide names and facts to support many of his most defamatory allegations.

"Any claims of questionable practices by current or former staff members at Trezevant High School and SCS that were reported to district leaders have been investigated or are currently under investigation. Should any evidence support wrongdoing by an employee, we certainly want that information brought to light so he or she may receive appropriate discipline.

"SCS remains strongly committed to providing the families at Trezevant High a high-quality, positive and supportive school culture, which is why the District announced additional resources, funds and new leadership for Trezevant earlier this year."

Reach Jennifer Pignolet at jennifer.pignolet@commercialappeal.com or on Twitter @JenPignolet.